1. Field of the Invention
This invention relates in general to the field of cantilever type electrical contactors, and more particularly to those that wipe (as xe2x80x9cwipexe2x80x9d is defined below) across the termination surface or area of a device under test while making contact therewith.
2. Description of the Prior Art
In the field of miniature electronic devices there are numerous devices, such as miniature capacitors having conductive end terminations, that require testing to insure the quality of their electronic capabilities. These devices are presently tested using one of two types of contactors where the contactors are used to temporarily connect to the conductive ends for the purpose of electrical measurement. The first type is a xe2x80x9cwipingxe2x80x9d or cantilever contactor and the second is an xe2x80x9cactuatedxe2x80x9d contactor.
A cantilever-type contactor typically has a flat spring metal arm which is canted or angled with respect to the device to be contacted. At the free end of the arm is a contactor. The contacting area of the device under test (hereinafter called a xe2x80x9cDUTxe2x80x9d) is moved, actually or relatively, such that the contactor rubs or passes, i.e., xe2x80x9cwipesxe2x80x9d, across the area and the cantilever arm is deflected slightly. The spring in the arm applies pressure on the contact area of the DUT, sufficient pressure for good electrical contact. This wiping technique can use one cantilever arm and one, opposite, stationary contact point, or two cantilever arms, one at each end of the DUT.
The wiping method, although simple and reliable, has certain drawbacks. The contacting pressure, supplied by the cantilever arm, needs to be controlled carefully. Too little pressure will result in poor electrical contact, too much pressure can damage the termination, i.e., the contacting areas of the device being contacted, particularly when the terminations are coated with a tin or tin/lead solder plating. Termination damage to the device is defined as any removal of, or serious injury to, the solder plating, which is typically only 100-200 micro-inches thick. The cantilever contact tip, being relatively stationary, wipes across the entire exposed length of the device termination, creating a relatively large mark on the termination, greatly increasing the chances of termination damage.
Also, due to the increasing miniaturization of electronic devices, minimal clearance exist between the surface of the holding fixtures needed to hold the DUT and the device terminations. The result is that the cantilever tips periodically come into contact with the holding fixture. Since the cantilever tip is relatively stationary, it is abraded by the test fixture material, which is typically FR-4 glass epoxy, or a similar non-conductive material, which tends to have a moderate or high abrasive quality. The cantilever tips become rough from this contact and tend to further damage the DUT terminations. Also, the contactor tips become dirty, either by oxidation or adherence of contaminants to the contact tips, or a combination of both. Access to the contact tips for cleaning is difficult due to the close proximity of the contact tips to the DUT and the device holding fixture(s).
The actuated contactor technique uses moving contact tips, usually in a reciprocating motion, which are brought into contact with the DUT. The contact tips are actuated for each test cycle, moved until they make contact with the DUT, then remain stationary during the measurement process. After measurement, the contacts are moved away from the DUT and the holding plate or fixture is indexed, bringing the next DUT into position for the next measurement. Actuated contacts can be made with very small tip sizes in order to reduce any marking of the termination ends of the tested device, unlike the wiping contact technique. Due to the high throughput of production testing equipment, this actuation cycle must be done at a very high speed and at rapid rates. For example, a component tester such as the Palomar Model 3300 would require 37,500 contactor actuation cycles per hour, running 150,000 parts per hour. If the components used for the actuation mechanism lasted 30,000,000 cycles, they would have to be replaced every 40 days, assuming 20 hours of machine run time per day. If the actuation time was only 10 micro-seconds in each actuation direction, the system throughput would be decreased by 10,000 parts per hour. Actuated contacts can also push or pull the DUT out of its holding plate/fixture, and the contact tips tend to be more expensive, requiring moving or flexible electrically conductive components, such as gold plated springs, or very flexible wire segments.
Prior art cantilever type contactors also include a roller supported by an axle that is, in turn, housed between a pair of spaced-apart flanges and held therein by an overhead axle clamp to form a rolling contactor. The flanges are supported by the cantilever arm and, when testing is under way, the arm and flanges are lowered to a point where the roller is brought into contact with the top of the device termination. The DUT is moved under the roller, making contact therewith, and test signals, passed through the device from the other end (or vice versa), are received in the roller and passed upward through the axle, then to the flanges, and into the arm for transmittal to a test device located at the remote end of the cantilever arm. Thus designed, contact between the roller and the DUT termination is a product of three distinct downward forces, to wit: the downward force of the cantilever spring arm, the downward force of the axle clamp, and the downward force of the axle against the inside rim of the roller. When measurement takes place, these three downward forces are balanced by the upward force of the DUT through contact between the DUT termination surface and the outer surface of the roller.
While the use of these rollers has ushered in a general improvement over the prior art of high speed device testing, the three combined forces often prove too severe for the DUT termination and cause damage to the surface of the termination. Once the surface is damaged, the device is no longer able to perform its electrical functions in high quality electronic environments and is relegated to other, low quality uses. Accordingly, there continues to be a need for a testing contactor that will provide rapid, positive contact with the DUT termination yet not be as positive in downward force as to cause damage to the termination surface.
In addition, the prior art contactors are in some cases, ganged together and set side-by-side in groups of four (4) or more so that four different DUTS could be brought into simultaneous contact with one set of four contactors to increase the throughput of the machine. The prior art does not provide adequate control to the level of the rollers causing one or more rollers to lie above or below another. To insure positive contact with the highest roller, the other rollers are pushed down harder to bring all the rollers, including the highest roller, into positive contact with the termination surfaces of their respective DUTs resulting in different pressures being brought to bear on the various devices. This difference in pressure often causes false readings on test equipment as well as damage to the DUT termination surfaces.
This invention is a contactor that will allow rapid and repeated electrical connection to the terminations of many types of DUTS with little or no damage or markings to their respective surfaces. The electrical contactor according to this invention is a significant advance over the prior art. It eliminates the damage done to the solder plating on the terminations of devices due to the xe2x80x9cwipingxe2x80x9d action of the cantilever type contactors and is simpler and has a longer life than the actuated type contactor. It is particularly useful in component handlers and testers for the processing and testing of electrical circuit components, for example ceramic capacitors. (As used herein the term xe2x80x9ccomponentxe2x80x9d refers to ceramic capacitors and any other electrical device having a form that allows it to be contacted by this invention).
This invention is a rolling contactor for providing electrical signal communication between a component terminal and a support structure for the rolling contactor, comprising a circular roller of finite thickness, forming an outer rolling surface and an inner, centralized hole, between two, spaced-apart side walls, for rolling across the termination surface of a DUT. A pair of circular spools of smaller outside diameter than the roller, each located adjacent one of the roller side walls and concentric thereto, is provided wherein each spool has formed therethrough a centralized hole for the support axle. An axle bracket is adapted to receive an axle clamp thereover and support the axle in a rotational position to allow the roller to rotate and press against the termination surface of the component. At least one conductive brush is provided that extends into contact with one of the spools in tangential arrangement to pick up the signals from the roller surface. Finally, an elongated spring arm extends between the axle bracket and the support structure, to complete the electrical path between the termination surface of the DUT, the roller and the spool in contact with the axle bracket through the conductive brush, and to provide spring pressure to press the roller against the termination surface.
While the contact force on the DUT of the prior art was always the greater of the forces required for electrical connection of the axle and inside rim of the roller or the connection of the roller and the DUT, the invention allows the DUT to encounter only the force needed for a reliable connection of the roller to the DUT. Contact forces that are needed for electrical connection internal to the invention, namely the force of the conductive brush against the spool, are not exerted on the DUT. Additionally, the conductive brush pushes upwardly against the spool, which, in turn, pushes the roller in an upward direction against the axle. This causes the bottom of the axle to be in contact with bottom of the inside rim of the roller in all states, whether the cantilever arm is exerting downward force on the roller or not. Any clearances between the axle and the inside rim of the roller are thereby removed. This is particularly valuable when the contacts are initially moved downward towards the DUT to determine the initial point of contact of the bottom of the roller to the DUT, since any xe2x80x9cplayxe2x80x9d in the fit of the inside rim of the roller on the axle is effectively removed.
This has significance to the ganged contactors by allowing them to be aligned more easily such that the new alignment reduces the overall difference between the highest and the lowest roller thus providing more of an average pressure on the four DUTs set side-by-side as aforesaid.
Accordingly, the main object of this invention is a contactor that exerts less pressure on an underlying DUT termination surface than those in the prior art. Other objects include a contactor that can be used and cycled for longer periods of time and test more DUTs than other, prior art devices, before having to be replaced; a contactor that may be used more consistently and display more accuracy than prior art contactors; and, a contactor that can be more accurately ganged to provide testing to a plurality of DUTs to increase throughput and output of the testing machines.
These and other objects of the invention will become more clear when one reads the following specification, taken together with the drawings that are attached hereto. The scope of protection sought by the inventors may be gleaned from a fair reading of the claims that conclude this specification.